crypto,all: allow to choose which crypto key algo are allowed

[MichaelMure]

Note

High Risk
Changes cryptographic acceptance policy and default behavior (empty DefaultKeySet), alters when did:key keys are validated, and fixes RSA multibase wire format—callers may break or see interoperability shifts until they register algorithms or pass WithKeySet.

Overview
Replaces the monolithic crypto/_allkeys decoder with a KeySet / KeyType registry so callers choose which algorithms (and RSA modulus sizes) are accepted. Each crypto/<algo> package exposes KeyType(); crypto/all blank-import registers everything into DefaultKeySet, which starts empty until you Register or import all.

DID resolution gains did.WithKeySet(...): did:key and did:plc decode embedded publicKeyMultibase only through the selected set, so mismatched policies fail resolution. did:key parse no longer validates the key until Document(). Multikey unmarshaling uses crypto.PublicKeyFromMultibase (default set).

RSA did:key multibase encoding/decoding switches from PKIX DER to PKCS#1 RSAPublicKey DER, aligned with the spec; KeyType can restrict allowed RSA bit lengths.

Tests add _ "crypto/all" where full algorithm support is needed and cover KeySet restriction for did:key, did:plc, and package-level crypto behavior.

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[Copilot]

Pull request overview

This PR refactors public-key decoding to be policy-driven via a pluggable crypto.KeySet, allowing callers to control which key algorithms (and for RSA, modulus sizes) are permitted during DID resolution. It replaces the previous “decode everything” approach (crypto/_allkeys) with opt-in registration (including a crypto/all convenience package) and wires the policy into did:key and did:plc resolution paths.

Changes:

• Introduces crypto.KeySet/crypto.KeyType, an initially-empty crypto.DefaultKeySet, and a crypto/all side-effect import to register all supported algorithms.
• Adds did.WithKeySet(...) and updates did:key + did:plc resolution to decode public keys through the selected key set (moving did:key validation from parse-time to Document()).
• Switches RSA publicKeyMultibase encoding/decoding to PKCS#1 RSAPublicKey DER (from prior PKIX/X.509 encoding).

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
verifiers/did-web/web.go	Documents that did:web does not apply WithKeySet during resolution.
verifiers/did-plc/plc.go	Decodes did:plc embedded did:key public keys via the resolution KeySet.
verifiers/did-plc/plc_test.go	Updates tests to opt into all algorithms via crypto/all.
verifiers/did-plc/document_test.go	Adds coverage verifying WithKeySet enforcement during did:plc resolution.
verifiers/did-key/key.go	Defers key decoding to Document() using the resolution KeySet; parse no longer decodes/validates keys.
verifiers/did-key/key_test.go	Updates tests for new did:key behavior and adds WithKeySet coverage.
verifiers/_methods/multikey/multikey.go	Switches Multikey JSON decoding to use crypto.PublicKeyFromMultibase (DefaultKeySet-governed).
options.go	Adds ResolutionOpts.keySet, accessor KeySet(), and did.WithKeySet(...).
document/document_test.go	Ensures tests register algorithms via crypto/all.
did_test.go	Adds WithKeySet tests and registers algorithms via crypto/all.
crypto/x25519/key.go	Adds x25519.KeyType() for KeySet registration.
crypto/secp256k1/key.go	Adds secp256k1.KeyType() for KeySet registration.
crypto/rsa/public.go	Changes RSA multibase decode/encode to PKCS#1 RSAPublicKey DER.
crypto/rsa/key.go	Adds rsa.KeyType(sizes...) to encode RSA size policy into a KeySet.
crypto/p521/key.go	Adds p521.KeyType() for KeySet registration.
crypto/p384/key.go	Adds p384.KeyType() for KeySet registration.
crypto/p256/key.go	Adds p256.KeyType() for KeySet registration.
crypto/keyset.go	Introduces KeySet, KeyType, DefaultKeySet, and helper decode APIs.
crypto/keyset_test.go	Adds tests for algorithm restriction and RSA size policy enforcement.
crypto/ed25519/key.go	Adds ed25519.KeyType() for KeySet registration.
crypto/all/all.go	Adds a kitchen-sink side-effect import to register all algorithms into DefaultKeySet.
crypto/_allkeys/allkeys.go	Removes the previous monolithic “all algorithms” decoder.

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Cursor Bugbot has reviewed your changes and found 2 potential issues.

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[cursor]

Tests omit key registration

Medium Severity

Resolution now decodes keys in Document() via DefaultKeySet, which starts empty unless algorithms are registered. These in-package tests call Document() without WithKeySet or a blank crypto/all import, so they fail where they previously passed because parsing used to decode keys eagerly.

 

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[cursor]

Multikey ignores KeySet policy

Medium Severity

Multikey JSON unmarshaling still calls crypto.PublicKeyFromMultibase, which always uses DefaultKeySet. WithKeySet on DID resolution only affects paths like did:key and did:plc, so a restricted resolution policy can be bypassed when verification methods are loaded from JSON via Multikey.

 

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